Inhibition of foaming in steam generation



United States Patent INHIBITION OF FOAMING IN STEAM GENERATION Carl E.Johnson, Westchester, llL, assignor to National Aluminate Corporation,Chicago, Ill., a corporation of Delaware N 0 Drawing. Application March7, 1956 Serial No. 569,958

The present invention relates to the inhibition of foaming in steamgeneration and more particularly to the prevention or reduction offoaming in steam generators operating under superatmospheric pressureand temperature conditions.

It is well known that in the operation of steam boilers, such as inrailroad locomotives, in electric power plants and the like, or in otherboiling operations where steam is formed, as for example, inevaporators, that the water therein, even though initially it showslittle tendency to foam, will, when the amount of total dissolved'solidsapproaches a relatively high concentration due to the production ofsteam, develop a very decided tendency to foam. This foaming of thewater in a boiler producing steam is characterized not only by anaccumulation of relatively stable froth or foam on. the surface of theboiler water but also by the formation at the heat transfer surfaces inthe boiler of extremely small steam bubbles. These minute bubbles showalmost no tendency to coalesce and the result is that the entire volumeof water in the steam generator is lifted in the form of so-called lightwater, which is actually an intimate mixture of boiler water and tinysteam bubbles. When this occurs, considerable quantities of boiler waterare physically carried out of the boilers or evaporators with the steam,thereby introducing solid matter into the steam lines and into theeventual condensate. disadvantages because it tends to contaminate andrestrict the steam lines, to plug or corrode the valves, to deposit onturbine blades, to plug and cause burning out of superheater tubes,andunder serious conditions may.

even impair the cylinders and piston rods of steam engines or otherwiserender the steam unfit for use. The j carryover is frequently due inpart, at least, to priming,

or what may be described as surging or boilinggover of the water.

One of the objects of this invention is to provide a new and improvedprocess for preventing the foaming and priming of steam generators, thusimproving the,

quality of the steam produced thereby.

' Another object is to provide new and improved compositions for addingto the water in a steam generator to prevent or reduce its'tendency tofoam. 7

Another object isto provide antifoaming compositions which are effectiveto prevent foaming when used 1n very low dosages.

Such carryover has many A further object is to provide highly effective.anti- I foam compositions which are readily and easily dispersible whenadded to the feedwater entering a steam generator. t p

Another object of this invention is to provideantifoam compositions inwhich the active effective ingredicuts are readily soluble in water atrelatively low tem-' W peratures (e. g., 75 F.), but decrease insolubility when An additional object is to provide new and usefulantifoaming compositions of an extremely high order of resistance todecomposition under the conditions prevailing in steam generation. Otherobjects will appear hereinafter.

In accordance with this invention it has now been found that there is aseries of compounds which may be broadly designated as high molecularweight trihydroxypolyoxyalkylene ethers of alkylene triols containing 3to 6 carbon atoms which are very effective in inhibiting foaming in thegeneration of steam from water under superatmospheric pressure andtemperature conditions."

oxide and ethylene oxide or mixtures of propylene oxide and ethyleneoxide, the relative proportions of propylene oxide to ethylene oxidebeing within the range from 9:1 to 1:9 and the condensation beingcarried to a stage such that the molecular weight is at least 1500. The

oxyalkylene groups apparently add on to the free hydroxy groups of thetriol to produce chains. It is possible that the reaction occurs to agreater extent at the primary hydroxyl groups than at the secondaryhydroxyl group of the triol. Since ethylene oxide has a molecular weightof 44 and 1,2-propylene oxide has a molecular weight of '58, thequantity of alkylene oxide required to produce a compound of a givenmolecular weight can readily be calculated. This quantity will depend tosome extent, of course, upon the relative proportions of the ethyleneoxide and propylene oxide. The products may be cogeneric mixtures ofaddition products and the present invention contemplates the employmentof such mixtures provided the average molecular weight is at 'least 1500as measured by the acetyl value and reckoning three free hydroxyl groupsper molecule.

In general, the mol ratio of alkylene oxide per mol of triol such asglycerine or 1,2,6-hexanetriol should be within the range from about30:1 to 3002-1 and especially good results have been obtained by theemployment of such addition products having an average molecular weightwithin the range from about 1500 to about 6000.

When the addition products employed for the purpose of the invention areprepared by adding a mixture of ethylene oxide and propylene oxide tothe initial triol such as glycerine or 1,2,6-hexanetriol, they arereferred to herein as trihydroxy mixed poly(oxythylene-oxypropylene)ethers of the triol. Excellent results are obtained in the practice ofthe invention when these compositions are prepared as described in U. S.Patent 2,733,272, have the oxyethylene groups from about 20 to about 80mol percent of the total oxyalkylene groups and have a minimum averagemolecular weight of at least 1500.

The invention also contemplates the use ofpolyoxyethylated-polyoxypropylated triols containing 2 to 6 carthe wateris heated to relatively high temperatures such as are employed in thegeneration of steam under superatmospheric pressures and thecorresponding tempera tures.

bon atoms in the initial triol which are prepared by first addingpropylene oxide, e. g., 1,2 -propylene oxide, to the initial triolfollowed by the addition of ethylene oxide.

As in the case of the mixed polyethers, the weight ratio of propyleneoxide to ethylene oxide should be within the range of from 9:1 to 1:9.

The addition products employed for the practice of the invention for themost part are liquids, although it is possible to employ compositionswhich are solids provided Patented Feb. 24, 1959 v in inhibiting thefoaming of water in a steamgenerator' will depend upon severalfactorsarnong them the percent of solids in the foaming liquid, thenature of the solids,

the alkalinity, temperature and pressure, the type and degree: ofcirculation in the steam generator, the rate of steam production and theamount of foam suppression desired. It is therefore impossible to stateany rigid rules for estimating the amount of the antifoam composition tobe employed. The amounts of the antifoam compositions employed in thepresent invention, however, are ex tremely small and for most purposessatisfactory results are obtained at dosages within the range of 0.001grain per gallon (g. p. g.) to 0.02 g. p. g, Within this range it willoften be found that an optimum foam suppressing effect occursat aparticular dosage. For example, in one series of tests as hereinafterdescribed, the optimum suppression of'foam on a water containing 5 0 g.p. g. of dissolved solids was obtained at a'dosage of 0.005 g. p. g.Since one grain per gallon corresponds to -17.1 parts per million itwill be recognized that the quantities of antifoam composition requiredfor the purpose of the invention are very small indeed and in general itcan be said thatquantities greater than 0.1 g, p. g. in the feedwaterwould seldom be required and depending upon the conditions of operationmight produce a less desirable result,

than a smaller dosage.

The tests to evaluate the invention were carried out in a Industrial andEngineering Chemistry, vol. 27, pages It was also equipped with anautomatic tion at the rate of 5 to 6 gallons per hour at 250 pounds persquare inch (p. s. i.) gauge pressure. A continual recording was made ofthe relative co nductivity of the condensate from the'boiler, andcontinual observations were made of the character of the'boili ng andtheamount of foaming as seen through the sight glasses. When the antifoamthus introduced continuously/with the feedwater was no "longer able toovercome the foaming tendencies brought about by the concentration ofdissolved solids in the boiler water, the foam height became greatenough to cause boiler water to be carried out of the boilerwith thesteam, and this end point of the test was determined both by observationthrough the sight glasses, and, particularly, by the abrupt increase inthe conductivity of the 4 EXAMPLE I e The test water employed in thisexample was prepared from a zeolite-softened Chicago tap water which,after '-the addition of various salts contained 30 g, p. g. of iNa SO 5g. p. g. of NaCl, 1 g. p. g. of Ca (as CaCO 1 g. p. g. of Mg (as CaCOand enough sodium bicarbonate to giveanM alkalinity (as NaHCO of 17 g.p. g. This water was then treated with 2. g. p. g. of chestnut organictannin and. various dosages of. the compositions to be tested' andevaporated in a test, boiler of the type previously described at 250 p.s, i. at the rate o f 5,gallonis per hour until gross carryoveroccurred.

A blankrun on this testwater under these test=conditions where noantifoam c omposititon was added to the 'water gave a carryover at atotal dissolved solids value of approximately 134 g. p. g.

The results obtained with various antifoam compositions in accordancewith the invention at various dosages were as follows:

Dissolved Solids at Carryover (a p. a)

Material Amount In the foregoing tests Composition A was atest-composition known as Dow Polyglycol 90-1 having a molecular weightin excess of 1500, and made by the addition of ethylene oxide andpropylene oxide to glycerol in a weight ratio of 90% ethylene oxide and10% 1,2-propylene oxide. This composition had a viscosity of 1225centistokes at 100 F.

Composition B was a composition known as Dow Polyglycol 19-350 made bythe addition of a mixture of ethylene oxide and propylene oxide toglycerol in the manner describedin U. S. Patent 2,733,272, the weightratioof propylene oxide to ethylene oxide being approximately 2:1 andthe reaction being carried out until the viscosity, was 350 centistokesat 100 F.

EXAMPLE II The test procedure was carried out as in Examplel v exceptthat the test waterwas a well water re-enforced with NaCl, NaHCO Na SOand Na CO togive a;con-,, centratable dissolved solids content of 210g.;p. g. with; an M alkalinity equal to 10% of the dissolved sol idsThis waterwas then treated with 3.0 g. p. g. of chestnutsteam, as shownin the continuous-recorder. Atthis end 7 point, a sample of the boilerwater was withdrawn from j the boiler and analyzed, andltheelfectiveness of the antifoam, expressed in terms of thetotaldissolved-solids con-. centration which it permitted the.b0iler; to.carry, was

noted.

By comparing the totaldissolved solidsvalue of a water... I

containing no added antifoam. composition iththe total i x i i iier hs.i l at a sq b ti qt i it dby te ely ns aa r.

dissolved solids; value of thewat er containing the antifoam.

organic tanninandthe antifoam tests were carriedout;

according to the test procedure previously described by; boiling thewater in a boiler at 250 p. s. i.vand at--a rate 1;: of 6 gallonsperhour until gross carryover was obtained.

In this series of tests a composition known as Dow.-

Polyglycol 15200-at a dosage of 0.005 ;grain per gallon gave a totaldissolved solids value at carryover of 1106 g. p.g.

Another composition within the scope of the invention,; namely, DowPolyglycol 15-500, under the same test con-.. ditions at a dosageof0.005 g. p. g. gave atotaldissolved 1, solids value at carryover of 2791g. p. g.

The Polyglycol 15-200 is a trihydroxy mixed poly.-...(oxyethylene-oxy-1,2-propy1ene) ether of glycerol made by adding amixture of ethylene oxide and 1,2-propylene oxide in an equal molarratioas described-in Example II of U. S.:Patent 2,733,272,-the mol ratio ofsaid oxides to.

said glycerolbeing 72:1 and the viscosity of the resultant-.-.-'

product .being approximately 200 centistokesat=-100. F;

'TheBolyglycol 15 500 is similarly preparedexcept-thata the mol ratio ofalkylene oxides to glycerol is 264:1 and l l 1 l product is around 489centi Parts per million Calcium hardness (as CaCO 178.0. Magnesiumhardness (as CaCO 185.0 Alkalinity (methyl orange) (as CaCO 1370.0Sodium chloride (as NaCl) 334.0 Sodium sulfate (as Na SO 1950.0 Tanninextract, dry"-. 51.0

EXAMPLE III This example illustrates the preparation ofpolyoxyethylated-polyoxypropylated glycerol suitable for the practice ofthe invention.

One pound of glycerine and 60 grams of an alkaline catalyst such as NaOHor KOH was charged to a pressure kettle, with good agitation and propertemperature controlling facilities. This mixture was heated to 120 C. to150 C. and then 1,2-propylene oxide was added maintaining a temperatureof 120 C. to 150 C. and pressure of 25 to 100 pounds per square inchgauge until 70 pounds of 1,2-propylene oxide per pound of glycerine wasadded. Samples were taken when 40, 50, 52 /2, 55 and 57 /2, 60, 62 /2,65 and 70 pounds of 1,2-propylene oxide per pound of glycerine had beenadded. To each of the above samples 0.35, 0.44, 0.51, 0.57, 0.62 and0.65 pound of ethylene oxide per pound of oxypropylated glycerine basematerial were added. In this way a series of 54 compositions. suitablefor the practice of the invention are prepared. These compositions arepreferably neutralized with glacial acetic acid to neutralize thecatalyst and stop the reaction.

As previously pointed out the oxyethylene groups in the oxyalkylatedtrihydroxy polyethers preferably represent from about 20 to about 80 molpercent of the total oxyalkylene groups. The optimum results appear tobe obtained with compositions in which the oxyethylene groups representfrom 33 to 60 mol percent of the total oxyalkylene groups. Especiallygood results have been obtained where the oxyethylene groups representabout 50 mol percent of the total oxyalkylene groups and there is anaverage of at least 50 oxyalkylene groups 'per glycerol nucleus.

Where the addition product employed in the practice of the invention ismade from glycerol, ethylene oxide and 1,2-propylene oxide, it has thefollowing structural n o onormxocntom).

in which as and y are integers such that the total average molecularweight is at least 1500, the weight ratio of 1,2-oxypropylene groups tooxyethylene groups is within the range of 9:1 to 1:9 and the oxyalkylenegroups can square inch and the corresponding temperatures. Excel lentresults have been obtained with the practice of the invention atpressures within the range of 100 to 300 pounds per square inch and thecorresponding tempera tures. The invention can also be used, however, incon nection with the generation of steam at much higher pressures andthe corresponding temperatures, as, for example, in stationary boilersoperating at pressures as high as 1000 to 1500 pounds per square inch.The compositions employed in accordance with the invention are elfectivenot only in inhibiting foaming but also in conditioning and improvingthe quality of the steam. For this purpose, they may be used in evensmaller amounts than the amounts required for the complete inhibition offoaming and priming.

The compositions employed in .the practice of the invention aredesirable when used in conjunction with other organic water treatingchemicals of the tannin and lignin types. On waters high in mangesiumsalts in which the magnesium in the boiler will generally be in the formof magnesium hydroxide, it is desirable that a suflicient amount of apowdered tannin, sodium lignin sulfonate or desulfonated lignin beemployed along with the antifoaming composition of the present inventionto nullify the effect of the magnesium hydroxide in selectivelyadsorbing the antifoam material. If this effect is not nullified themagnesium hydroxide may take the antifoam material out of the boilerwater so that the full antifoam action is not exerted by the antifoamcomposition. However, when an organic material such as a tannin isadded, magnesium hydroxide appears to lose its ability to interfere withthe action of the antifoam agent. Inasmuch as most boiler feedwatersencountered will have varying amounts of magnesium salts present, it isdesirable that the compositions used in the practice of the presentinvention be mixed with the hydroxylated organic compound such astannin, sodium lignin sulfonate or desulfonated lignin, prior toaddition to the boiler feedwater. In general, when the polyoxyalkylatedtriol is incorporated with tannins, sodium lignin sulfonate anddesulfonated lignins prior to adding it to the boiler feedwater, thequantity of the polyoxyalkylated triol is within the range of 0.5% .to12% by weight of the total composition and the total quantity oftannins, sodium lignin sulfonate and/or desulfonated lignins is withinthe range of about 50 to about 97% by weight of the composition.

A few examples will serve to illustrate the preparation of suitabledry-appearing, dispersible compositions adapted to be added to boilerfeedwater in the practice of the invention.

Example A: Parts by Weight Polyoxyalkylene triol of Examples I, II andIII 3 Desulfonated li nin 97 The resultant composition is prepared byadding the polyoxyalkylated triol to the dry pulverized ligninderivative in a putty chaser type mixer. It is a dry, freeflowingcomposition readily dispersible in water.

, Example B: Parts by weight Polyoxyalkylated triol of Examples I, IIand III 3 Refined tall oil 2 Desulfonated lignin 95 This composition isreadily and completely dispersible in water, the residual alkalinity ofthe lignin derivative serving so convert the refined tall oil to soapwhen the composition is added to water and the strong foam inhibitingaction of the polyoxylalkylated triol serving not only to abate the foamproduced during steam generation but also overcoming any foaming actionthat might ordinarily be caused by the tall oil soap.

It will be understood that the tennis, sodium lignin sulfonate and/ ordesulfonated lignins are not necessarily addition of the latter to thefeedwater. Where it is 'de'-' sirable to use tannins, sodium ligninsulfonate and/o1 Table Tannins, Sodium, Lignin Sulfonate and/rDesulfonated Lignins, Grains per Gallon in Boiler Water Magnesium-Grainsper Gallon in Boiler Water (expressed as OaC Os) As will be apparentfrom the foregoing description, the compositions employed in accordancewith the invention do not all give the same results and from thatstandpoint are not necessarily equivalents.

ing and condition steam on a very economical basis.

In the specification and claims the expression boihng undersuperatmo-spheric pressure and temperature cond1- tions is intended toinclude and cover those conditions where steam is generated attemperatures above 100 C.

and at superatmo-spheric pressures. The expression addition productssubstantially insoluble in said boiler waterat the temperature of steamgeneration refers to thecharacteristic of the addition product whichcauses it to separate into two phases when a solution thereof-is heated1 from ordinary temperatures around C. to the temperature at which steamis generated. The quantity of the addition product actually employed forthe purpose Some of these compositions are exceptional in their foaminhibitingproperties and their use makes it possible to inhibit fo'am--of the invention may be so small that this insolubility is diflicult toobserve but any-of the polyoxyalkylene triols of the type hereindescribed whendissolved in a 1% -solu tion in water at ordinarytemperatures and heated to 100 C. at atmospheric pressure with theseparationv of an in soluble phase is satisfactory for the purpose ofthe invention.

The invention is herebyclaim'e'd as follows:

1. A method of generating steam from a boilerwater having a tendency tofoam on boiling which comprises.

dispersing in said watera quantity of an addition product of an alkylenetriol containing 3 to 6 carbon atoms, propylene oxide and ethyleneoxide. in which theweight ratio of propylene oxide to ethylene oxide iswithin the range of 9:1 to 1:9, the average molecular weight of saidaddition product is at least- 1500 and said addition product issubstantially insoluble insaid boiler water at the temperature of steamgeneration,- thequantity of said dispersing in said water a quantity ofan addition product of analkylene triol containing 3 to 6 carbon atoms,propylene oxide and ethylene oxide in which the weight ratio ofpropylene oxide to ethylene oxide is within the range of 9:1 to 1:9, theaverage molecular weight of said addition product is at least 1500 andsaid addition product is substantially insoluble in said boiler water atthe temperature of steam generation, the quantity of said additionproduct being effective to inhibit the tendency of said water to foamon'boiling, and boilin'gthe'resultant aqueous dispersion undersuperatmospheric pressure and temperature conditions.

3. A method'of generating steam from a boiler water having a tendency tofoam" on boiling which'co'mprises dispersing'in said water a quantity ofanaddition product of an alkylene triol containing 3'to 6 carbon atoms,propylene oxide and ethylene oxide in which the weight ratio ofpropylene oxide to ethylene oxide is within the range of '9:1 to 1:9,the average molecular weight of said addition product is at least 1500and said addition product is substantially insoluble in said boilerwater at the tem perature of steam generation, the quantity of said addition product being effective to inhibit the tendency of said water tofoam on boiling, and heating the resultant aqueous dispersion-atpressures within the range of 100' to 1500 pounds per squareinch and thecorresponding temperatures.

4. A method as claimed in claim l in whichthe oxy-. ethylene groupsrepresent from about 20 to about 80' mol percent of the. totaloxyalkylene groups in said addi tion product.

5. A'method as claimed in claim 1 in which the oxyethylene groupsrepresent from 33% to of the total oxyalkylene groups in said additionproduct.

6. A method as claimed in claim 1 in 'whichsaid addition product has amolecular weight within the range from 1500 to 6000.

7.. A method as claimed in claim 1 in which said addition productcontains a mol ratio of alkylene oxide per mol of triol within the rangefrom about 30:1 to 300:1.

8. A method of generating steam from a boiler water having 'a tendencyto foam on boiling which comprises" dispersing in said water a quantityof a trihydroxy mixed poly (oxyethylene-oxy-1,2-propylene) ether ofglycerol in' which the oxyethylene groups represent from about 20' toabout mol percent of the total oxyalkylene groups, there'is an averagefrom 30 to 300 oxyalkylene groups per'glycerol nucleus, and the averagemolecular weight is atleast 1500,. the quantity of said addition productbeingeffective to inhibit the tendency of said water'to foam on boiling,and boiling the resultant aqueousdis per'sion under superatmosphericpressure'andtemperature" conditions.

a 9. A method as claimed in claim 8 in which the oxy- "ethylene groupsrepresent. about 50 mol percent of the total oxyalkylene groups in saidpolyether.

References Cited in the file of this patent UNITED STATES PATENTS2,575,276 Jacoby Nov. 13, 1951 2,727,009 Jursich Dec. 13, 1955 2,733,272Horsley an; Jan."31,1956

1. A METHOD OF GENERATING STEAM FROM A BOILER WATER HAVING A TENDENCY TOFORM ON BOILING WHICH COMPRISES DISPERSING IN SAID WATER A QUANTITY OFAN ADDITION PRODUCT OF A ALKYLENE TRIOL CONTAINING 3 TO 6 CARBON ATOMS,PROPYLENE OXIDE AND ETHYLENE OXIDE IN WHICH THE WEIGHT RATIO OFPROPYLENE OXIDE TO ETHYLENE OXIDE IS WITHIN THE RANGE OF 9:1 TO 1:9, THEETHYLENE OXIDE IN WHICH THE WEIGHT SAID ADDITION PRODUCT IS AT LEAST1500 AND SAID ADDITION PRODUCT IS SUBSTANTIALY INSOLUBLE IN SAID BOILERWATER AT THE TEMPERATURE OF STEAM GENERATION, THE QUANTITY OF SAIDADDITION PRODUCT BEING EFFECTIVE TO INHIBIT THE TENDENCY OF SAID WATERTO FOAM ON BOILING, AND HEATING THE RESULTANT AQUEOUS DISPERSION TO THEBOILING POINT.